[Clayart] over stacked kilns

mel jacobson melpots at mail.com
Sat Oct 29 14:26:45 UTC 2022

We have new people on clayart all the time.
This is one topic that cannot be repeated enough.
"over stacking a kiln leads to bad firing."

Colleges and Art centers are doing it all the time.
It becomes a pride thing..."got every pot in the studio
in one firing...give me a gold star."

All kilns need space to let the fuel, heat move around
the kiln. Gas or electric, same thing.

Nils Lou and I did a great deal of study on this topic.
The worst ecology in firing is bad pots that need to be fired
again, or thrown out. A bad firing may lead to the entire
load being thrown out.  Save those last 10 pots for another firing.
Think of the value of a load of pots. My big kiln 45 cubes, means
a thousand dollars in my pocket. Bad firings first waste your money,
then the ecology of wasted fuel.

No major industry in the world would tolerate wasted fuel. Every BTU is
measured. PH. D. engineers are paid a great deal of money to monitor fuel loss.
Most all people understand the concept of pollution.  It is the potter that
is polluting and does not know it,  that makes me crazy.

Some things to consider.
One, do not pack shelves together. Leave space for heat flow.
Start the stack a couple of inches off the floor. Stagger everything.
Keep shelves from blocking the flue.
Leave a thumb width between pots.  yes, at least an inch.
Leave space for the cones to get normal heat. Do not stick
the cones in a tight space inside a group of pots.
Remember, the heat inside of bottles and closed space must match
the outside heat...You have to wait for it...and down firing makes
sure the inside is totally heated.

Poorly designed bag walls block the flow of heat. In a well designed
gas kiln you do not need bag walls. Original bag walls where used
to keep wood and fly ash off the pots.

Always fire with bright blue flame. Dirty orange flame does not aid
reduction. Reduction is when the flue/damper is pushed in, gas pressure
matches the damper, back pressure in the kiln can be seen coming from
the peep hole. Always put your cones in the same place, the same peep hole.
Do not move your pyrometer around. I have  a sign on my pyrometer "Do not move, EVER".
the wires are stapled to the space around the kiln.

Room ventilation is critical. Use fans. (goodwill has many for sale.)
Make sure that cool air is filling your kiln room.

There is a great deal of very old information that is sort of 1938 engineering.
It is 2022, match your firing with modern information.

website: www.melpots.com

More information about the Clayart mailing list